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Vermont's governor has signed a bill making it the first U.S. state to ban fracking, the controversial practice to extract natural gas from the ground.

"This is a big deal," Gov. Peter Shumlin said Wednesday. "This bill will ensure that we do not inject chemicals into groundwater in a desperate pursuit for energy."

Shumlin said fracking contaminates groundwater and the science behind it is "uncertain at best." He said he hopes other states will follow Vermont's lead in banning it.

Fracking, or hydraulic fracturing, has unleashed a boom in energy production in the United States by allowing the extraction of oil and gas from shale rock. Supporters say it has reduced the country's oil imports, boosted natural gas production and provided thousands of jobs.

Most major oil companies are now involved in shale oil and gas production, including Exxon Mobil, Royal Dutch Shell and BP.

But the process has also raised fears of ground water contamination and is suspected of causing mild earthquakes.

Fracking involves injecting water, sand and some chemicals deep into the earth to crack shale rock, which frees oil and gas. Critics fear the chemicals are seeping into the groundwater.